Many methods exist to measure body composition but none proven to be accurate, safe and applicable to patients with abnormal fluid balance. It is hypothesized that 2 new methods based on electrical impedence, called TOBEC and BIA, can accurately determine body composition despite increases in extracellular fluid volume due to disease. 10 renal and 10 liver disease patients will be measured with TOBEC and BIA before & after fluid removal and compared to TBW measured by deuterium & extracellular fluid by bromine dilution.